Field of the Invention
The present invention relates to a polymer for a resist under layer film composition to be used in a fine patterning by the multilayer resist method in the manufacture process of a semiconductor apparatus, a resist under layer film composition containing the polymer, and a patterning process using the composition.
Description of the Related Art
As LSI advances toward high integration and high processing speed, miniaturization of pattern size is progressing rapidly. Along with the miniaturization, the lithography technology has achieved a fine patterning by shortening wavelength of the light source and selecting an appropriate resist composition accordingly. As for such a composition, positive photoresist compositions used for a monolayer are mainly selected. The monolayer positive photoresist composition allows a resist resin to have a skeleton having an etching resistance against dry etching with chlorine- or fluorine-based gas plasma, and provides a switching mechanism that makes an exposed part soluble, thereby dissolving the exposed part to form a pattern and subjecting a substrate to be processed to dry etching using the remaining resist pattern as an etching mask.
However, when a pattern becomes finer, that is, a pattern width is reduced, without changing the thickness of a photoresist film to be used, resolution performance of the photoresist film is lowered. In addition, pattern development of the photoresist film with a developer causes a pattern collapse because a so-called aspect ratio of the pattern is excessively increased. Therefore, a photoresist film has been thinned along with the miniaturization of a pattern.
On the other hand, for processing a substrate to be processed, a method of processing the substrate by dry etching using a pattern-formed photoresist film as an etching mask is generally used. In practice, however, there is no dry etching method capable of providing an absolute etching selectivity between the photoresist film and the substrate to be processed. Therefore, the resist film is also damaged and collapses during processing the substrate, so that the resist pattern cannot be transferred to the substrate to be processed precisely. Accordingly, along with the miniaturization of a pattern, higher dry etching resistance has been required in a resist composition. On the other hand, however, to enhance the resolution, a resin to be used for the photoresist composition has been required to have low absorption at the exposure wavelength. Accordingly, as the exposure light shifts from i-beam to KrF and to ArF to have a shorter wavelength, the resin also shifts to a novolac resin, polyhydroxystyrene, and a resin having an aliphatic polycyclic skeleton. Actually, an etching rate during processing the substrate becomes higher under the dry etching condition, and recent photoresist compositions having a high resolution tend to have a low etching resistance.
Thus, a substrate to be processed has to be dry etched with a thinner photoresist film having lower etching resistance. The need to provide a composition used in this process and the process itself has become urgent.
A multilayer resist method is one of the solutions for these problems. This method is as follows: a middle layer film having a different etching selectivity from a photoresist film (i.e., a resist upper layer film) is placed between the resist upper layer film and a substrate to be processed; a pattern is formed in the resist upper layer film; the pattern is transferred to the middle layer film by dry etching using the upper layer resist film pattern as a dry etching mask; the pattern is further transferred to the substrate to be processed by dry etching using the middle layer film as a dry etching mask.
One of the multilayer resist methods is a three-layer resist method, which can be performed with a typical resist composition used in a monolayer resist method. For example, this three-layer resist method includes the following steps: an organic film containing a novolac resin or the like is formed, as a resist under layer film, on a substrate to be processed; a silicon-containing film is formed thereon as a resist middle layer film; a usual organic photoresist film is formed thereon as a resist upper layer film. Since the organic resist upper layer film exhibits an excellent etching selectivity ratio relative to the silicon-containing resist middle layer film when dry etching is performed with fluorine-based gas plasma, the resist upper layer film pattern can be transferred to the silicon-containing resist middle layer film by dry etching with fluorine-based gas plasma. According to this method, even when a resist composition which is difficult to form a pattern having a sufficient film thickness for directly processing the substrate to be processed or a resist composition which has insufficient dry etching resistance for processing the substrate is used, the pattern can be transferred to the silicon-containing film (resist middle layer film). Further, dry etching using an oxygen gas plasma or a hydrogen gas plasma enables the pattern to be transferred to the organic film (resist under layer film) containing a novolac resin or the like, which has a sufficient dry etching resistance for processing the substrate. As to the resist under layer film, many materials are already known as disclosed in Patent Document 1.
In recent years, many studies are made on a semiconductor apparatus having a novel structure such as a multi-gate structure. Accordingly, there is a growing need for a resist under layer film having more excellent filling and planarizing properties than conventional one. For example, when a substrate to be processed used as a base has a fine pattern structure such as hole, trench, and fin, gap-filling property is required to fill the gap of the pattern with a resist under layer film without space. In addition, when the substrate to be processed used as a base has a step or when both of a pattern-dense portion and a no-pattern region exist in one wafer, the film surface is necessary to be planarized by the resist under layer film. By planarizing the surface of the under layer film, fluctuation in film thickness of a resist middle layer film and a resist upper layer film formed thereon is controlled, whereby the reduction of a focus margin in lithography or a margin in the processing step of the substrate to be processed thereafter can be inhibited. In addition, to completely remove the resist under layer film used in filling and planarizing by dry etching after processing the substrate, a resist under layer film having a dry etching property different from the above films, for example, a resist under layer film having dry etching rate higher than that of the resist upper layer film is required in some cases. Furthermore, it may be also necessary to process the substrate by wet etching with a chemical reagent. In this case, the resist under layer film used as a processing mask also requires a resistance to a wet etching liquid.
Detailed explanation is now given about the background that materials for the wet etching process is required in the multilayer resist method. In the cutting-edge semiconductor apparatus, technologies such as three-dimensional transistor and through interconnection have been used to improve performances of the semiconductor apparatus. In a patterning process for forming such a structure in the semiconductor apparatus, patterning by the multilayer resist method has also been applied. Such a patterning sometimes requires, after pattern formation, the step of removing the silicon-containing resist middle layer film without causing damage to the pattern. If the removal is inadequate, more specifically, if the wafer is subjected to a subsequent manufacturing process while an object to be cleaned still remains thereon, yield of device production is surely lowered. Accordingly, as a device progresses toward miniaturization, a higher cleaning degree is required in the cleaning step. However, main constitutional elements of the conventional silicon-containing resist middle layer film and that of the semiconductor apparatus substrate are both silicon in many cases. Therefore, if one wishes to selectively remove the silicon-containing resist middle layer film by dry etching, it is difficult to suppress damage to the semiconductor apparatus substrate because both the constitutional components are similar. This problem cannot be resolved by wet etching using a usual hydrofluoric acid type peeling solution. Thus, as a peeling liquid that does not cause damage to a semiconductor apparatus substrate, a wet etching liquid composed of an alkali aqueous hydrogen peroxide called Standard Clean-1 (SC1), which has been generally used in the semiconductor manufacturing process, is considered to be used. In this case, resistance to an alkali aqueous hydrogen peroxide is rather required in the resist under layer film.
As to the resist under layer film composition, for use in manufacturing a semiconductor apparatus, having a high dry etching rate and capable of planarizing a stepped substrate, for example, Patent Document 2 discloses a material containing a polymer such as polyglycidyl methacrylate. Moreover, as to the resist under layer film composition, for use in manufacturing a semiconductor apparatus, having a high dry etching rate, Patent Document 3 discloses a material containing a copolymer produced from monomers such as (meth)acrylic acid and glycidyl (meth)acrylate; and Patent Document 4 discloses a material containing a cross linking agent and a copolymer produced from monomers such as hydroxypropyl methacrylate. However, these known materials do not have sufficient filling and planarizing properties to meet the requirements for the manufacture of a cutting-edge semiconductor apparatus.
As to the resist under layer film composition having resistance to an alkali aqueous hydrogen peroxide, Patent Document 5 discloses a material that contains polymer having an epoxy group and a carboxyl group protected by a vinylether compound (acetal-protected ester), for use in a 2-layer process not using a resist middle layer film. However, this material has insufficient planarizing property and thus not suitable for patterning of a substrate to be processed having unevenness and steps, which particularly has high requirements in the cutting-edge process.
As mentioned above, it has been desired to develop a resist under layer film composition, for use in the manufacture of a semiconductor apparatus, having excellent filling and planarizing properties and dry etching property as well as compatibility with wet etching process (i.e., alkali aqueous hydrogen peroxide resistance), and a patterning process using the same.